Ever more stringent emissions regulations have driven the compression ignition engine industry to adopt increased fuel injection pressures. One area of concern as a consequence of increased injection pressures relates to potential fatigue in the sac region of the fuel injector nozzle tip component. The sac region is often the thinnest pressure containment metallic layer, and also defines the nozzle outlets that extend between an interior volume of the fuel injector to the combustion space of the engine. The sac region will typically cycle through extreme high pressures with each engine cycle.
One strategy believed to have promise in strengthening fuel system components is to induce compressive residual stress on the inner surface the component. While a number of different strategies are possible for inducing compressive residual stress, an autofrettage process can be effective in inducing compressive residual stress on the interior surfaces of pressure vessels. For instance, Chapter 4 from Adis Basara's PhD. dissertation, Evaluation of High Pressure Components of Fuel Injection Systems Using Speckle Interferometry (2007), teaches sealing one end of a fuel line in order to perform an autofrettage process. Thus, an effective autofrettage process for a fuel injector nozzle tip may require that the nozzle outlets be sealed during the autofrettage pressurization procedure. Because the autofrettage pressures are so high, finding a robust production strategy for nozzle tips in a factory setting can be problematic.
The present disclosure is directed toward one or more of the problems set forth above.